This invention is generally directed to the routing of calls in a telecommunication network and is more specifically directed to the selection of an intermediate switch through which a call is to be routed between an originating switch and a destination switch.
Various techniques have been applied to control the routing of calls through a telecommunication network. A dynamic non-hierarchical routing arrangement is described in Ash U.S. Pat. No. 4,345,116 wherein each switch is equipped to match a received directory number and a corresponding destination switch. Based on the identification of a destination switch a plurality of predetermined direct and alternated routes for reaching the destination switching system is stored in a table. Although this system provided an advance, it suffers from disadvantages such as requiring a plurality of control messages to be passed within the system in order to determine if the predetermined paths stored in the routing table is available to handle a call. During times of heavy loading, these messages created significant traffic within the system, especially when a number of alternate paths had to be sequentially attempted due to heavy loading.
A real time network routing (RTNR) technique is described in Ash U.S. Pat. No. 5,101,451. In this arrangement an intermediate switch is selected by comparing traffic loading data of trunks of each of the intermediate switching systems between the origination switch and the destination switch. The selection of an intermediate switch among the potential intermediate switch candidates is based upon the loading of circuits associated with the intermediate switches. This technique has the advantage of responding to outages of switching systems or transmission facilities by routing around the systems or facilities, and further provides the advantage of normalizing the distribution of calls added to the system since lightly loaded intermediate switches are selected for handling calls.
The RTNR technique generally assumed that each switch within the network contained the necessary distributed intelligence to make a routing path decision. The technique also required the ability to obtain information concerning the loading of other switches upon demand in order to make such decisions. Thus, such a network is best suited for a system in which the switches utilized within the system are substantially identical or at least homogenous with regard to network administration and control. Systems which utilize a variety of types of switches which do not utilize identical control signaling or traffic load data makes the RTNR technique more difficult to effectively implement. The advantages of the RTNR technique do not extend to the routing of calls outside of the RTNR switching network, i.e. the routing of calls which must pass to another network such as in another country or a switching network controlled by a different company. Further, although the loading of intermediate switches is considered by the RTNR method, an independent consideration of the loading of the switch independent of the transmission facility paths associated with the switch is not taken into account. Thus, a switch which becomes loaded to near capacity by demands for processing in addition to the processing requirements associated with the volume of calls being handled may result in the inappropriate selection of a switch. Thus, there exists a need for even further advancements in network routing in order to further improve and achieve additional efficiencies beyond the prior control systems.